Character recognition apparatus



Dec. 8, 1964 P. H. HOWARD 3,160,853

I CHARACTER RECOGNITION APPARATUS Filed Dec. 21, 1959 3 Sheets-Sheet l D. C. GENERATOR -l8 CHANNEL REDUCTION CIRCUITS 22 LINEAR AMPLIFIER cmcuns ,24 FILTER cmcuns ,26 SiGNAL DURATION cmcuns w-- I V INTEGRATION CIRCUITS TIMING CONTROL' T A0 cmcun A DIGITAL TRIGGERS I l t 54 TIMING cmcuns BUFFER TRIGGERS V REGISTER MATRIX A8 7 mzcosumou cmcuns 4o 42- CHECKING cmcun CHARACTER REGISTER RECOGNITION OUTPUT INVENTOR PHILIP H. HOWARD AGENT Dec. 8, 1964 P. H. HOWARD 3,160,853

CHARACTER RECOGNITION APPARATUS I Filed D80. 21, 1959 3 Sheets-Sheet 2 50 INTEGRATOR IPPING 12 77 CIRCUIT un 64 11 as 73 $1 5e so I 15 DELAY SLOPE' I cmcun INDICATOR 61 74 78 o DELAY $1155 TR FIG. 4

Dec. 8, 1964 P. H. HOWARD 3,

CHARACTER RECOGNITION APPARATUS Filed Dec. 21, 1959 s Sheets-Sheet :5

I 1os l l g T 2 1- a F iii FIG. 5

character energization amplitude.

Patented Dec. 8, 1964 3,169,353 CHARACTER RECOGNITIUN APFARATUS Philip H. Howard, Apalachin, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Dec. 21, 195%, fier. No. 861;,lll7 9 Claims. (Cl. 340-41463),

This invention relates to character recognition apparatus and more specifically to apparatus for determining the duration of information bearing signals produced upon the scanning of an energized character bearing surface.

Numerous types of character recognition systems have een disclosed including both single channel and multichannel systems, and digital and analog type systems. The present invention is particularly adaptable to the system employing, in a plurality of channels, means for linearly scanning acharacter to be recognized and setting up in a storage matrix, by means of the multichannel signals, a representation of a character scanned by the multichan nel scanning means, and employing means for recognizing the character representation set up in the storage matrix. Apparatus of this type is disclosed in the patent application of Eckelman, Hennis and Larson, Serial No. 804,996,

filed April 8, 1959.

The present invention represents an improvement over the invention disclosed in the above-mentioned patent application and relates to the portion of the system disclosed therein in which the signals in each channel of the multichannel systems are analyzed to determine whether or not the signals are representative of black or white areas on the character bearing surface being scanned.

When the character forming areas are energized magnetic areas and the scanning means is magnetic scanning means, variations in the magnetic head output signal result from loss of contact between the heads. and the document. Such out of contact conditions occur due to creases or folds in the document, embossing of the printing of the document, bounce or chatter between the pressure pad and the read head. Variations in output signal intensity are produced by variations in ink density and variations in While these problems can be partially overcome by increasing pressure between the document and the read head by means of loaded back up devices, this expedient results in excessive head wear and serves to only partially overcornethe problems involvedl t In certain types of character recognition systems; it is essential that the time duration of information bearing signals be employed to provide'accurate representation of the length of the character forming area producing the I signal. .Variations in signal amplitudes as wellas other considerations which will be hereinafter described have a very substantial influence on the apparent length of information bearing signals. i

It is accordingly'the primary object of this invention to provide apparatus responsive to the output signal of character scanning means for providing signals which'are accurate representations ofthe. length of the" character increment scanned by the scanning means.

It has been observed that as. a document carrying energized magnetic characters is moved out of contact with magnetic scanning means, the high frequency components of the resulting signal are the first to'disappean therefore it is necessary to devise a signal duration indication apparatus that minimizes the need for high frequency. signals in the output of the scanning means.

It is thus a further object of the invention to provide a signal duration indicating apparatus that is substantially insensitive to high frequency signals. a When characters to be read are printed in ink, there are inevitably involved certain printing tolerances which must be granted to the printers for the production of printed documents at reasonable costs. These tolerances give rise to unwanted signals and to voids in desired signals as well as to deviations in the apparent locations of character edges. These conditions, resulting from normal printing tolerances, can affect the scanning means output analyzing apparatus to produce undesirable variations in matrix patterns produced thereby adversely affecting the operation of the recognition logic by which the characters represented in the matrix are recognized as the characters scanned. Characters otherwise presented such as for example for optical scanning present similar nonunifo'rmities to the scanning means.

It is the principal object of this invention to provide means which will operate to produce signals giving ac curate indications of the time duration of character forming areas scanned by scanning means and at the same time to provide apparatus which is relatively insensitive to spurious peaks in the output signals as well as to gaps in the signal.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular :description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

' In the drawings:

FIGURE 1 is a block diagram showing the various component parts of the embodiment ofthe invention disclosed herein.

FIGURE 2 is a block diagram showing in greater detail one of the component parts shown in FIGURE 1 which includes an integration circuit and a clipping circuit.

FIGURE 3 is a circuit diagram of the integration and clipping circuits shown in FIGURE 2. v

FIGURE 4 is a circuit diagram of the delay and slop indicating circuits shown in FIGURE 2. i

FIGURE 5 is a timing diagram showing waveforms appearing at various locations in the apparatus during reading of a character.

The various elements involved in the embodiment of the invention disclosed herein will first be described in a general manner in connection with FIGURE 1 in which there is shown those components which are old, having been previously disclosed in the above-mentioned patent application, and those components which are new andare more fully disclosed herein as representing an improvement over the above-mentioned patent application. p

In FIGURE .1,:th ere isshown at 10,"a fragmentary portionof a document or other surface forming means carryand 16, respectively, positioned to. scan the character as itpasses thereby. f The write, head 14 is poweredffr oma .DQC, source v18 magnetic and'thus operates to magnetically polarizethe material in the ink forming the indicia' 12.

.The read head It: is actually aplurality or read heads positioned adjacent .toone another to provide multichannel scanning of characters passingthereunder. It is 'desirable to provide write and read heads'of sufiicient length with respect to the. vertical height of the character to be read to insure scanning o'f the entire height of each character even though successive groups of characters maybe-dis placed vertically with respect to each other or printedl on various horizontal lines. Accordingly, a single extended write head is used and, in conjunction therewith, a read" head is employed having, in the arrangement. describecLa number of heads which is an even multiple of the mini- 7 mum number of heads desirably employed to fully scan I a single character. Gutputs from the multichannel read head 16 are delivered to channel reduction circuits'Zil.

In the embodiment of the invention described herein, 7

the channel reduction circuits receive outputs from twenty magnetic heads in the read head 16 and reduce these to ten channels for subsequent manipulation. The'ten channels represent a sufficient length of the read head' id to insure the multichannel scanning of the entire height of a character 12.

While various types of character printing, character energizing and character scanning means may be employed, for certain purposes magnetic printing, magnetic energizing and magnetic scanning are preferred. Regardless, however, of the particulararrangement employed, the essential objective is the production ofsignms on each of the ten channels representing horizontal scanning through a character to be recognized. It will also be evident that the selection oftenchannels is arbitrary depending upon the configuration of thecharacters to be identified aswell as the total number of characters to be recognized. As shown in FiGURE 1, each of the ten channels form cuits 28, the digital-triggers 3th, the buffer triggers 34, as

Well as the register matrix 36 and the recognition circuits 38 as Wlll be hereinafter described.

The timing circuits control the transfer of information from the integration circuits 2% successively through the digital triggers 3t and the butter triggers 34 to successive ing the output fronrthe channel reduction circuits 2% is delivered to a corresponding plurality of amplifier circuits 22. These amplifiers are linear amplifiers. The outputs of the amplifier circuitsZZ are delivered to filtercircuits 24. These circuits are "bandpass filters passing, for

example, frequencies from one thousand cycles toZQ. a

The linear amplifier circuits 22 are linear within thisband range. I Circuits of these types are well known and may in fact be combined inone unit by means of circuitry Well knownintheart.

The outputsof the filter circuits 24 are delivered to signal duration circuits Edwhichrepresent the essential elements of novelty inthis invention'and will be herein after described in greater detail in connection with FIG- URES 25. At-t-his time it is sufficient to note that the output of thesignal duration circuits is provided by a' tri er which indicates. whether at an given interval the input signals received from the read head elements are indicating-black or white, i.e.,-indicating whether or not the signals received are intormationbearing signals.

- The outputs or the signal duration circuits 26ers delivered to integration circuitsid, The integration circuits and all of the circuits shown thereafter in FlGURE "l have'been fully set forth-in the above-mentioned patent application and need not be described'indetajl herein.

The integration circuits 2% function to provide for successive inte rations when a black indieatin si nal' exists pei'at on ot a timing ci r'- columns of registers in the register matrix 36 during each successive character increment. At the end of the character scanning intervai,-this control will have provided in the register matrix, a representation of the character scanned.

checks to confirm the recognition of one character and not inore than one character, and generates inconjunction with the timing circuit 32, a reject signal it less than one character or more. than one character has been recognized.

In FEGURE 1,- there is alsoprovided, as indicated at 115, means for sensing'the leading edge of a character bearing surface, such as a card, sheet, or other document formin eans. .Thedocumcnt sensing means 15 serves to provide an output pulse in response to'the leading edge of a document and this pulse is employed to insure pr per settings of various components of the circuitry prior to the commencement of a character reading cycle.

through a plurality of integration timeintervals. The time f intervals'are determined by V -cuit32..f -f

,The outputsot theintegration circuits aredelivered'to -digital trigger'sfiti after'eachj of the integration time inter- -vals'; Une trigger is provided for each of the ,tenchannels 5 and the digital'trig'ger in each chann l ever integration 'in"thatchannel hasprbceeded to' a thresh oldvalue. U on turnin on of'a'di i ltri er,its inte ration -c'ircuit' is reset in preparation fora next successive integration cycle.

Each of the-ten digital triggersfiil when'on, isernployedto turn on arespective butterv trigger 34 in its channel, 5

The turning on of the .;.follovving manner.

buffer trigger is controlled .in' the Outputs of the digital triggers SLGJare delivered to al timing control circuit'iil which actswhen at least two digital triggers are on simultaneously to initiate'operati'on of a timing circuit 3?.., It is'considered, When two digital. trig, gers have ibeen turned on by" black indications in their respective channels, thatthi's is'suflicientevidence of the arrival of a character to be 'recognized, and the operation .iof'the jtiming circuit fizmay then beinitiated. Opera- ,tion of the timing eir-cuit s'e'rves to define character incref flinentsand to control the operation of the integration ciris turned on when;

' ter being scanned.

From the foregoing, it will be evident that character recognition apparatus of this type requires circuitry capable of accurately locating the character front in order that'the. timing apparatus iwill producecharacter incremental time intervals properly coincident with the charac- Furthermore, the apparatus must provide accurate qua-ntizing ot-character line lengths in order that both the character. front and the length of a character line in one horizontal channel through the character, as produced by the multichannel sensing means, will be accurately measured for transmission to the character matrix. a v

A third consideration is that the out-of-contact signal as the in-contact signal. I

When the characters being scanned have been energized by"rneans of tlieDC. source; and the polarized magnetic ink passes under a read head, the head will produce a drp/dtoutput in the form ofa positive pplsein response tothe leading'ed'ge of a character line ands negative pulse ,inresp s to the trailing edge,ot-ajcharacterline.- The zslope of thepulse is-a functionjofthe amplitude'lot the character energization and the distance between. the read-f .ing head andjthema'gnetic ink, and is thus ,aifect'edsubstantially by any outrofscontact condition between the readin'ghead and the surface o'fthe document carrying the printed indicia and also by the density .and magnetic characteristics of the inhforming the character being scanned. High frequency components-of theoutput are j attenuated moreithan low frequency components'as'. the

out-of-contact distance is'increased. j g

V he amplitude'of thefpulse isa fun'ction'ofithe em g'ization signal level which is substantially. uniform, the

inkjdensity which ma vary substantially and the out ofl eontactcondition if any exists;

The signal duration circuits indicated at 26 in FIG- URE 1, must befcapableof responding to a vWiderange of pulse shapes, i.e.,'puls elslope and amplitude conditions and to produce in res'ponsefito these 'pulses accurate indications of the length ofthe. character forming lines producf'ingthesignal.

An accurate. indication of line-length; is. obtained by measuring the time'betwecn the positive and negative must be interpreted with the same accuracy of response delaying this measurement and combining the delayed measurement with the output of a circuit integrating the dip/dz signal.

The presence of magnetic ink is indicated whenever the integrator level exceeds a fixed threshold value. However, due to the wide range of pulse shapes appearing in the d/dz signal, the period of time that the integration output exceeds the threshold value is not an accurate indication of character line length.

As will be described in greater detail, the integration portion of the device alone is not adequate as a signal duration indicator because it does not give an accurate measure of time. On the other hand, the peak detector alone is not adequate because spurious signal pulses and voids frequently occur during the reading of a character line and these would give rise to indications of unwanted short lines and to long lines as being a multiplicity of shorter lines. However, both of these circuits acting together are capable of giving an accurate indication of the presence and time duration of a character line.

In FIGURE 2, there is indicated generally at 26, the

signal duration indicating circuitry employed in one of the ten channels of the signal duration circuits shown at 26 in FIGURE 1.

The input to this circuit at terminal 56 is taken from the output of the amplifier and filter circuits in FIG- URE I. These signals are dp/dt pulses which have been filtered by the l-to-ZO kc. band filter. This input is de-' livered to an integrator circuit 52, the output of which is delivered to a clipping circuit 54. These two circuits will be hereinafter described in detail in connection with FIGURE 3.

At this time, however, it is noted that the input signal at terminal 55) is indicated on line ll of FIGURE 5. *On

line I.of FIGURE 5, there is represented, as a square wave signal, ink densities to which the scanning head is responding to produce the signals appearing on line II. The various portions of these signals will be hereinafter described. At this time, however, it should be noted that line TH represents the outputs of the integrator circuit 52 which is delivered to the clipping circuit 54. The clipping level is indicated at $9 in line III. Line IV shows the idealized square wave signal produced by the clipping circuit 54 ofFIGURE 2 in response to the output of the integrator shown online 111 of FIGURE 5.

, In FIGURE 2, there is also shown a delay circuit 56 which receives the input taken at terminal 50 and serves to delay this input and then deliver the delayed signal to a slope indicator 6%. The delay circuit is conventional and well knownrto those skilledin the art and thus need not be described in detail. herein. The details "of one .form of slope indicator'are shown in FIGURE 4 and will be described later. In FIGURE 5, the line VI shows the output of the slope indicator in response t'o a delayed input'wave which is shown on line V, this 'wave being identical to the wave shown'in line II'except for the delay time 1. k

The integration output on ,line 55 in FIGURE 2, is

delivered to one input of a two-input AND circuit 77' via line 72 and delivered through an inverter 64 and line 71. 2 0 one input of a two-input AND circuit'fifi.

when black areas are in the present application at 28 in FIGURE 1.

The output of the slope indicator 6%, on line 61, is

delivered via a capacitor '76 and line 74 to theother input of AND circuit 78 and through an inverter 63, capacitor 75 and line 73 circuit 77 to the other input'of AND The outputs of the AND circuits 77 and :78 provide,

the on-side and off-side inputs respectively to a trigger] {it which forins'the signal duration trigger. The off-s ide output of trigger 853 indicates the presence of a white or the absence of. acharacte'r indicating signal. the output at terminal 81 is a square Wave output with the signal down when the white areas are being read Thus,

The functioning of the circuits of FIGURE 2 can best i be understood by examination of the signals shown in' FIGURE 5. As has been previously described, the waveform shown on line I of FIGURE '5 represents ink patterns where the amplitude of the waveform is represent-ative of ink density and the horizontal length of the pulses shown is proportional to the time that the ink is under the sensing head. The pulse indicated at 82 is a pulse of normal amplitude and normal duration. The pulse indicated at 83 is of high amplitude and normal duration. The pulse indicated at 34- is high amplitude and short duration. The pulse indicated at 85 is of normal amplitudeand long duration but varies in amplitude during the central portion thereof resulting from either embossing of the ink into the document during printing or to squeezing out of ink whereby excessive quantities of ink exist at the edge of the character and relatively less ink exists inthe central region of the printing. The patterns indicated at 86 and $8 are of approximately normal time duration and amplitude separated by a small ga 87 indicating a void in the printed area 86-88.

The waveform of line II shows the filtered do/dt pulse output from the magnetic sensing head which has scanned the ink pattern shown in line I. This waveform is the input to the signal duration indicator circuits previously described. It is important to note that the distance between the positive and negative peaks of this waveform is equal to the distance between the'begin'ning and the end of. the respective ink patterns of the waveformsrof line I when the time duration of the ink pattern is sufliciently. long to provide a region of; linear signal 91 in line 11. Thus, for example, the pulses resulting from the ink pattern 82 are spaced apart by a time equal to the time duration of the ink patterned, whereas, the pulses resulting from ink pattern 84,are spaced apart by a time duration substantially greater than the time duration of the ink pattern 84..

The minimum. distance between the positiveand negative peaks isdetermined by the upper cut-ofl frequency of the filter circuit previously described. The amplitude of the filter signals is attenuated for short duration ink patterns such as 84f V The waveform on line III represents the output of the integrator circuit which is responsive to the waveform of line ll. \Vnile the area under each integrator pulse is: proportional to the area of the respective ink pattern, the

amplitude. of the integrator pulse 98 is greatly reduced because of the short time duration ofthe ink pattern 84.

It should be noted that themagnetic sensing device is a 'diiferentiator and therefore the integration process should producethe original waveform except for a constant.

out of contact with the documentand this filtering. cannot be eliminated. The filter circuit 24 shown in'FIG f I URE -1 makes' it possible to treat all signalsas ,though they were sensed out of con-tact and the signal duration- III by'setting a threshold level as is indicated bythe dotted line 99. The output of the ciipper'circuit is positive, if, and only if, the integrator output level exceeds the threshold level. This function can be accomplished with a high gain saturating"- amplifien operating about a threshold. The output of the clipper is shownon line j However, departure'from ideal reconstruction of the first waveform is due to the action of the.fil-ter circuit 24. Some filtering results from the fact that the head is s r p the trigger 157 on. Trailing edge signals, when diiferentiated, will turn trigger 157 off.

The output from the trigger, as it changes state, is supplied as previously described to the AND circuit 77 and 78 where the combination governs the signal duration trigger.

As previously explained in connection with the integrator and clipping circuits, the actual form of the slope indicator is immaterial, and the disclosed arrangement is exemplary.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. Character recognition apparatus comprising multichannel scanning means for scanning characters and producing a scanning signal in response thereto, quantizing means for each of said channels for determining whether successive increments of said scanning signal are indicative of scanned character-forming means, and means responive to said quantizing means for identifying a character scanned, each of said quantizing means including means for filtering from said scanning signal frequencies above av predetermined upper cut-off value, integrating and clipping means responsive to said filtered signal for producing a first output signal when and only when the amplitude-time integral .of said filtered signal exceeds a predetermined amplitude, means responsive to beginning and ending portions of said filtered signal for producing a delayed second output signal indicative of the duration of said signal, and means responsive to said first and said second output signals for signaling the scanning of a character-forming area.

2. Character recognition apparatus comprising multichannel scanning means for scanning magnetic characters and producing a scanning signal in response thereto, quantizing means for each of said channels for determining Whether successive increments of said scanning signal are indicative of scanned character-forming means, and means responsive to said quantizing means for identifying a character scanned, each of said quantizing means including means for filtering from said scanning signal frequencies above a predetermined upper cut-E value, integrating and clipping means responsive to said filtered signal for producing a first output signal when and only when theamplitude-time integral of said filtered signal exceeds a predetermined'amplitude, means responsive to beginning and ending portions of said filtered signal for producing a delayed second output signal indicative of the duration of said signal, and means responsive to said first and said second output signals for signaling the scanning of a character-forming area. 7

3. Character recognition apparatus comprising multichannel scanning means for scanning polarized magnetizable characters and producing output signals in response thereto, filter means, one for each channel, connected to said scanning means and eiiective to pass said scanning signal components below a predetermined upper .frequency cut-ofi value, quantizing means one for each channel, connected to. said filter means for determining whether successive increments of said filtered signal in each channel are indicative of scanned character-forming areas, and analyzing means connected to said quantizing means for identifying characters scanned, said quantizing means including integrating means in each channel responsive to said filtered signal for producing a first output indicative of the amplitude-time integral of said filtered signal, delay diiferentiator means for each channel connected to said filter means for providing a delayed second output signal indicative of the beginning and ending of each characterforming area, and logiccircuit means for each channel connected to said integrating means and said delay ditfer entiator means and effective to combine said first and said second signals to supply an output signal when said filtered signal begins and terminates with predetermined values of said amplitude-time integral. ,7

4. Character recognition apparatus comprising multichannel scanning means for scanning polarized magnetizable characters and producing output signals in response thereto, filter means, one for each channel, connected-to said scanning means andeffective to pass said scanning signal components below a predetermined upper frequency cut-01f value, quantizing means, one for each channel, connected to said filter means for determining whether successive increments of said filtered signals in each channel are indicative of scanned character-forming areas, and analyzing means connected to said quantizing for each channel, connected to said filter means for providing a delayedsecond output signal indicative of the beginning and the endingof each character-forming area, and logic circuitlmeans governed by said integrating and limiting means and by said delay differentiator' means for providing a signal output between the times that said second signal from said delay differentiator indicates the onset of a character-forming area, provided there is. a first output signal from said integrating and clipping means, and the time that said second signal from said delay differentiator means indicates the leaving of a character-forming area, provided there is no first output signal from said integrating and clipping means.

5. Character recognition apparatus comprising multichannel scanning means for scanning magnetically polarized characters. and producing output signals in response thereto, filter means, one for each channel, connected to 7' said scanning means and effective to pass said scanning signal components below a predetermined upper frequency cut-off value, quantizing means, one foreach I channel, connected to said filter means for determining Whether successive increments of said filtered signals in each channel are indicative of scanned character-forming areas, and analyzing means connected to said quantizing means for identifying characters scanned, said quantizing means including integrating and limiting means, one for each channel, connected to said filter means, and responsive to said filtered signal for supplying therefrom a first output signal indicative of the portion of the amplitudetime integral of said filtered'signal exceeding a predetermined threshold value, a delay means and a difie'rentiating I means, one for each channel, connected to said filterv means and effective to provide a" delayed and differentiated second signal in response to said filtered signalsthey delay time being in excess of the duration-of permissible low density areas in said character-forming areas, and logic circuit means governed by said integrating and limiting means and by said delay ditferentiator means for pro:

'viding a signal output between the times that said second signal from said delay' differentiator. indicates the" onset of a character-forming area, provided there is a first output signal from said integrating and clipping means, and the time that said second signal from said delay differentiator means indicates the leaving of a character-forming area, provided there is no first output signal from said integrating and clipping means.

6. Character recognition apparatus comprising multichannel scanning means for scanning magnetically polarized characters and producing output signals in response thereto, filter means, one for each channel, connected to said scanning means and effective to pass said scanning signal components below a predetermined upper frequency cut-01f value, quantiz'ing means, one for each 1 i l channel, connected to said filter means for determining Whether successive increments of said filtered signals in each channel are indicative of scanned character-forming I areas, and analyzing means connected to said quantizing means foridentifying characters scanned, said quantizing means including integrating and limiting means, one for each channel, connected to said filter means, and responsive to said filtered signal for supplying therefrom a'first output signal indicative of the portion of the ampiltudetime integral of said filtered signal exceeding a predetermined threshold value, a delay means and a differentiating means, one for each channel, connected to said filter means and effective to provide a delayed and differentiated second signal in response to said filtered signals, the delay time being in accordance with said upper frequency cut-off value, and logic circuit means governed by'said'integrating and limiting means and by said delay differentiator means for providing a signal output between the times that said second signal from. said delay differentiator indicates the onset of a character-forming area, provided there is a first output signal from said integrating and clipping means, and the time that said second signal from said delay dilferentiator means indicates the leaving of a character-forming area, provided there is no first output signal from said integrating and clipping means. 7. Means for accurately indicating the duration of a time interval denoted by electrical pulsesat the beginning and ending of the interval, comprising, in'combination,

integrating means for receiving said pulses and integrating the pulses, clipping means connected to said integrating means and efiective to supply a first constant amplitude signal therefrom during the time thatthe output of said integrating means is greater than a predetermined threshold value, delay means connected to receive said pulses and to provide delayed pulses in accordance'with the received pulses, differentiating means connected to said deyl lay means and effective to provide-a second slopeindicating signal in accordance with the changeof slope of said delayed pulses as the peak of the delay pulses occurs, and logic. circuit means connected to said clipping means and said difierentiating means and effective to provide an" output beginning at the time ofpe'ak amplitude of the delayed beginning pulse, provided there is a first outputsignal from said clipping means, and ending at the time of peak amplitude of the delayed ending pulse, provided there is no first output signal from said clipping means.

8. Means for accurately indicating the duration of a time interval denoted by a beginning pulse having one polarity and an ending pulse of theopposite polarity, comprising, integratingmeans connected to receive said pulses and to provide an output signal proportional to the amplitude-time integral of said pulses, clipping circuit means connected to said integrating means and effective to provide a constant amplitude output signal during the interval in which the integrated outputof said integrating means corresponding to said beginning pulse is greater than-a predetermined threshold value, delay means connected to receive said beginning and ending pulses and effective to delay said pulses by a predeterminedtime interval, differentiator means connected to said delay means and effective to diflferentiate said delayed beginning and ing pulse and no output is provided from said clipping circuit means, and output circuit means connected to said first and second logic circuit means. a I

' 9. An arrangement as claimed in claim 8, iniwhich said output circuit means comprises a bistable device set to one condition by said first outputand set to the other condition by said second output.

. References Cited in the file of this patent UNITED STATES PATENTS Flory et al. Oct. 28, 1952 2,963,683 Demerctal. Dec. 6, l960 FOREIGN PATENTS 1,174,001 France Mar. 5, 1959 Great Britain Nov. 6, 

1. CHARACTER RECOGNITION APPARATUS COMPRISING MULTICHANNEL SCANNING MEANS FOR SCANNING CHARACTERS AND PRODUCING A SCANNING SIGNAL IN RESPONSE THERETO, QUANTIZING MEANS FOR EACH OF SAID CHANNELS FOR DETERMINING WHETHER SUCCESSIVE INCREMENTS OF SAID SCANNING SIGNAL ARE INDICATIVE OF SCANNED CHARACTER-FORMING MEANS, AND MEANS RESPONSIVE TO SAID QUANTIZING MEANS FOR IDENTIFYING A CHARACTER SCANNED, EACH OF SAID QUANTIZING MEANS INCLUDING MEANS FOR FILTERING FROM SAID SCANNING SIGNAL FREQUENCIES ABOVE A PREDETERMINED UPPER CUT-OFF VALUE, INTEGRATING AND CLIPPING MEANS RESPONSIVE TO SAID FILTERED SIGNAL FOR PRODUCING A FIRST OUTPUT SIGNAL WHEN AND ONLY WHEN THE AMPLITUDE-TIME INTEGRAL OF SAID FILTERED SIGNAL EXCEEDS A PREDETERMINED AMPLITUDE, MEANS RESPONSIVE TO BEGINNING AND ENDING PORTIONS OF SAID FILTERED SIGNAL FOR PRODUCING A DELAYED SECOND OUTPUT SIGNAL INDICATIVE OF THE DURATION OF SAID SIGNAL, AND MEANS RESPONSIVE TO SAID FIRST AND SAID 